Larger scale multi-story buildings are typically constructed primarily of steel and concrete. Floors in such buildings are typically constructed by spanning steel joists between structural walls and laying a metal pan or decking across the tops of such joists. The decking forms a flat surface onto which concrete is poured. Generally, the bottoms of the joists form the framework from which ceilings are hung.
Although such flooring systems are common, there are a number of difficulties associated with them. First, such systems generally allow only for floors of a uniform thickness. This in and of itself is a problem, especially when dealing with adjacent suites having different ceiling heights. Furthermore, a great deal of time, effort and money must be expended to obtain the required sound and fire protection between adjacent suites in such buildings, and between adjacent floors or stories of the building.
In such conventional systems, large gaps or airspaces are formed between the tops of the walls on which the joists sit and the underside of the metal decking which sits on top of the "joist shoes" of the joists. These joist shoes are formed by the ends of the top chords of such joists, and angle irons welded to the undersides of this portion of the top chord. One such gap is formed between each pair of adjacent joists. Depending on the size of the joist shoes, these gaps are typically between 2 and 12 inches high, and extend along the length of the support wall. Such gaps are customarily filled with rock-wool, foaming products, fire-tape and/or double layers of gypsum board. The filling of these gaps is typically done manually from underneath the poured floor, and is accordingly labour intensive and costly. Often, this job is done poorly, leading to failed fire code inspections necessitating costly repairs. Even when done correctly, this time consuming filling of such gaps does not leave a particularly sound and fire-resistant floor and wall between suites.
There have been a number of composite concrete and steel floor systems suggested which ameliorate this gap problem somewhat. For example, in U.S. Pat. No. 4,454,695, which issued in 1984, Person discloses a composite floor system including a plurality of joists which have a top chord which allows metal decking to be placed not atop the joists, but between them. Poured concrete embeds the top chords of the joists. Similar systems are disclosed in U.S. Pat. Nos. 4,700,519 and 5,544,464.
With these systems, the gaps between the tops of the supporting walls on which the joists rest and the underside of the metal decking are reduced, although not eliminated. However, such systems have associated with them other difficulties which render them inadequate for use in some situations. For example, because the metal pans used in such systems do not rest on top of the joists themselves, but rather between the joists on angle irons which form the top chords of the joists, sections of metal pan must be carefully cut to identical lengths in installing such systems. This is time consuming. Furthermore, it is often necessary to move one or more joists by a few inches to accommodate between-floor services such as plumbing. When one joist is moved, two metal pans of different lengths must be custom-cut. This leads to wastage of material.
These prior art composite floors have one first her significant disadvantage in that they transmit vibrations exceedingly well. The steel joists, being embedded within concrete along their entire lengths, form part of the floor itself. Thus, a vibration caused by, for example, a washing machine operating in one suite can be transmitted throughout the entire floor of the building.
To overcome this vibration problem, composite floor systems often employ more concrete than would otherwise be necessary to dampen vibration. This of course increases the weight of such floors, which may require shoring while concrete is curing. Shoring adds to the floor cost and to construction time. Excess concrete may also require that the building be built on stronger foundations. In some areas, ground or soil conditions may militate against such heavier buildings. Also, higher profile joists are required to support the heavier floors. Accordingly, fewer floors can be built in a building of a given height.
Additionally, when concrete floor slabs are kept relatively thin, the placement of plumbing and other between-floor services is less time consuming and problematic. Conventionally, in a thicker floor, hollow pipes or "cans" must be put into place when the floor is being poured to provide apertures for between-floor services such as plumbing. The placement of these cans is critical and such cans are commonly placed in the wrong location, necessitating costly and time consuming movement of between-floor services to match the incorrect placement of the cans. It is also labour intensive and costly to finish the concrete floor surface around these cans. This may results in a poor quality floor surface. Apertures may be made in a thinner floor by drilling or "coring" after the concrete is poured.
There is accordingly a need for a floor system which overcomes the problems of gaps or airspaces between adjacent suites, and which does not have the disadvantages of composite floors in which joists are embedded entirely in the concrete which forms the floor.